Block copolymers comprising a poly(arylene ether) block and a polysiloxane block are known materials that are useful components of various thermoplastic and thermoset compositions. Their polysiloxane content makes them particularly useful as flame retardant additives. They can also be employed as compatibilizers to stabilize otherwise poorly compatible blends of polysiloxanes with aromatic polymers, such as polystyrenes, poly(arylene ether)s, aromatic polyesters, aromatic polyamides, and aromatic polyimides.
Some known methods for preparing poly(arylene ether)-polysiloxane block copolymers involve the linking of pre-formed poly(arylene ether) and polysiloxane groups to each other. For example, in U.S. Pat. No. 4,871,816 to Percec et al., silyl hydride-terminated polysiloxane blocks are linked to vinyl-terminated polyarylene polyether blocks via a hydrosilylation reaction. Thus, these known methods involve at least three steps, the first step to form a poly(arylene ether) block with reactive terminal functionality, the second step to form a polysiloxane block with at least one end group capable of reacting with the poly(arylene ether) reactive terminal functionality, and the third step to covalently link the poly(arylene ether) and polysiloxane blocks.
It would be efficient and economically advantageous to prepare poly(arylene ether)-polysiloxane copolymers with fewer processing steps, and some efforts have been made toward this end. For example, Banach et al. in U.S. Pat. No. 5,357,022 have reported the oxidative coupling of 2,6-xylenol (2,6-dimethylphenol) and a silicone macromer having terminal phenol groups. However, attempts to reproduce the reaction conditions of Banach et al. have resulted in products in which much of the phenol-terminated silicone macromer is not covalently linked to a polyphenylene ether block and the isolated product as a whole has a relatively low intrinsic viscosity (typically about 0.2 deciliter per gram). The reaction products of Banach are therefore of limited use as flame retardant additives or compatibilizers, because they tend to segregate into two distinct and poorly compatible phases, one consisting largely of polyphenylene ether homopolymer, and the other consisting largely of unreacted phenol-terminated silicone macromer.
In U.S. Patent Application Publication No. 2009/0318635, Carrillo et al. report a method for making poly(arylene ether)-polysiloxane block copolymers having polysiloxane incorporation efficiencies as high as 91 to 100 percent. However, in Carrillo's working examples, these high efficiencies were only achieved when the polysiloxane was 5 weight percent of the total monomer charge. When the polysiloxane loading was increased to 20 weight percent of the total monomer charge, the polysiloxane incorporation efficiency dropped to 26 to 72 percent.
There is therefore a need for improved methods of synthesizing poly(arylene ether)-polysiloxane block copolymers with improved incorporation of the polysiloxane into the desired block copolymers, particularly at high polysiloxane loadings.